Electric hammer



Jan. 31, 1939. R. T, FETHERSTON I ELECTRIC HAMMER Filed July 24, 1936wV///lllllllllllllrllrl INVENTOR W T m a. yam

ATTORNEY Patented Jan. 31, 1939 ELECTRIC HAMMER Robert T. Fetherston,Milwaukee, Wis., assignor toMilwaukee Electric Tool Corporation,Milwaukee, Wis., a. corporation of Wisconsin 7 Application July 24,1936, Serial No. 92,309

This invention relates tof portable percussion 7 tools such as electrichammers.

be of the type requiring a commutator. The motor V In such tools thedriving-motor must ordinarily runsat very high speeds in order toprovide the necessary power with light weight, and at each blow of thehammer there is transmitted to the body of the tool and to the motor asevere jar or shock. This shock results even during normal operation,and at times is greatly increased when the ram overruns, for any ofvarious reasons, and

' strikesthe end of thechamber in which itreciprocates. Anysuch'repeated jar or shock is seriously detrimental 'to the operation ofthe motor commutator, causing sparking and undue wear, together with theloss of power in heating, and various other objectionable results.Similarly the vibration and shock isdetrimental to va- :rious' otherparts of the device including the switch." -It is very objectionable tothe hand of theoperator who guides the tool. Also it tends to loosen allthe bolts, screws or rivets etc. hold-' ing the various parts together.Moreover the revibrations of increasing amplitude;

i The invention consists in the construction shown, described, andclaimed herein, and in such variations or modifications of the structureshown and described as may be equivalent to the structure of the claims.

Like reference characters apply to the same parts throughout thespecification, and in the drawing:v

' Figure 1 is a perspective view partly in section of a portableelectric hammer incorporating the invention.

Figure 2'is a longitudinal section of the same Y device.

Figure 3 is a modified hammer structure also incorporating theinvention.

The machine as shown in Figs. 1 and 2 includes a plurality of housingsgenerally denoted by the numerals I and 2. The housing I is providedwith a hand grip portion 3 in which is housed a switch 4 havingatrigger-like operatingfmember 5. Cables 6, I lead from the switch to amotor,

carried by housing I, generally denoted by the 4 Claims. (01. 125-33)numeral 8, which is of high speed, series wound type having a rotor 9and a commutator I0 for supplying current to the rotor, there beingcommutator brushes such as II retained in the usual or any suitablemanner in brush holders such as I2, to be spring pressed against thecommutator.

Housing I also carries reduction gearing including the pinion I3 carriedby an extension of the motor shaft and a gear I4 fixed on a shaft I5.

End plates I6, ll of housing I carry the bearings for pinion I3 andshaft I5, and are removably fixed with the main casting I8 in part bythe means of screws such as I9 and in part by the bolts 20, 2I whichextend through suitable flanges at the adjacent ends of housings I and 2to fasten the housings together, there being another bolt 22 which doesnot extend through.

The housing 2 carries a shaft 23 coaxially alignediwith the shaft I5 andcoupled to be driven from shaft I5 by a member 24. At its other end theshaft 23 carries a cam element 25 against which a cam member 26 iscontinuously pressed by a spring 21, the spring seating at the one endon an abutment member 28 fixed with housing 2, s and seating against thecam member 26 at its other end.

- Cam member 26 is fixed with a reciprocating hammer member 29. At theend of the housing I is fixed a tool receiving socket or member 30providing a bore 3| through which the shank of a tool such as 32 mayextend to be struck by the reciprocating member 29.

During revolution of shaft 23 from the motor 8 through the mechanismdescribed the cam element 25, revolving against a cam face 33 of the cammember 25, presses the member 25 and the reciprocating member 29 to theright of Fig. 2 against the resistance of spring 21. The cam member 26is of a form such that after traveling to the right the reciprocatingmember 29 is suddenly released to be thrust to the left in Fig. 2 by thespring, thereby delivering a hanmier blow against the end of the toolretained in the socket or bore 3I. At times, and particularly if thereis not suflicient resistance to the tool the member 29 may overrun tostrike the interior face of the member 30. The speed of the motor andthe driving connections to the shaft 21' are such as to deliver a greatmany of such blows per minute at substantially equal intervals.

The shock and vibration incidental to the release of the member 26, andto the striking of the member 29 against the end of the tool or againstmember 30 are, unless'prevented, transmitted to the housings I and 2 andto each of the various elements of the device. Unless prevented, suchvibrations cause sparking between the brushes II and commutator II] ofthe motor 8 and the various other objectionable results previouslymentioned, particularly if the vibrations tend to be amplified or builtup by the timed repetition of the hammer strokes.

To reduce the shock of individual blows and to prevent the building upof the amplitude of the vibration caused by repeated blows, there ispro-,

vided the following structure. A member or gasket 35 of suitable shockabsorbing and vibration damping material such for instance as rubber isinterposed between the adjacent end faces of the housings I, 2, thebolts 20, 2|, 22 passing through the gasket. In addition, underneath theheads of each of the bolts 25, 2 I, 22 there are additional gasket orwashers of the shock absorbing or resilient material, such as 35, 31,38. The bolts 20, 2 I, 22 are seated solidly against the end plate I! ofhousing I, whereby to effect a predetermined space underneath the boltheads of such value as to provide a predetermined initial compression ofthe shock absorbing material of the several gaskets. By the means of thedescribed construction each of the housings I, 2 is cushioned on shockabsorbing and vibration damping material in either direction of itsmovemen't, set up by the hammer operation, relative to the other housingand each of the housings and every part carried thereby is effectivelycushioned against individual blows and the structure is such as toprovide efiect-ive damping against building up of vibration effects byrepeated blows. Inorder to provide added surface bearing against thewashers 35, 31, 38 the bolts 20, 2|, 22 are each provided with washersor bearing plates such motor and to provide for the brushes andcommutator substantially the same life as would be obtained in a toolwhich was not subjected to the shock of the hammer blows, and to greatlyincreasing the 'e-fiiciency and power of the motor, and to greatlyreduce the tendency of the motor and its commutator to overheat. Thereis also a material reduction in the shock and vibration transmitted tothe hand of the operator, and substantially no tendency for the switchand various 'fastenings' to be loosened or damaged.

It is to be understood that the gaskets, as here shown may be made ofvarious materials, and in some instances some or all of the gaskets maybe replaced with springs of suitable form and position.

The hammer shown in Fig. 3 includes a motor, not shown, havingcommutators as indicated at '4'! and housed within a casing 42, therebeing a pinion '43 fixed on the motor shaft and engaging a gear 44having fixed thereon an eccentric 45 which reciprocates a crank 45.Fixed with crank '46 is a rod 4'! which reciprocates a plunger or hammermember 48, guided in a housing 49, the member 48 being cushioned ineither direction by springs 50, 5I. Carried at the lower end of member48 is an anvil or hammer 52 positioned'to strike the end of a tool-53 ateach reciprocation of crank 46, the tool being removably retained in amember 53a.

At the joint between the member 530, and housing 49 there is provided aresilient gasket,

and resilient washers 55, 56 associated with the bolts 51, 58 in amanner and for a purpose and result similar to the resilient gasket 35and washers 36, 31 of the hammer shown in Figs. 1, 2.

The motor housing 42 and housing 49 are removably fixed together at ajoint indicated at 54, and it is also contemplated that such joint may,if desired, be provided with resilient gaskets and washers (not shown)such as those shown for joining the motor and hammer housings I, 2 ofFig. 1, and for joining the member 530, and housing 49 of Fig. 3.

With the structure disclosed any shock which tends to move one of thehousings I, 2 relative to the other primarily further compresses one ofthe opposed resilient devices consisting respectively of the gasket 31and of the collective gaskets 36, 31,38. The other resilient device issimultaneously relieved of some of its initial compression set up by thebolts 25, 2I, 22. This cushions the shock and, in addition, aconsiderable portion of the force of the blow is absorbed or damped outby the deformation of the resilient devices and, in part by movement ofone or both of the housings I, -2. Such rebound as occurs from 'a shockin the one direction is similarly cushioned and clamped by thecorresponding but opposite action of the resilient devices in the otherdirection, and the result of the. combined damping of both the initialand rebound shocks is tosubstantially completely cushion and damp outany individual shocks irrespective of the rate at which they mayberepeated, and toentirely prevent any building up or amplificationthereof which might otherwise occur for shocks repeated at regularintervals.

What is claimed is:

-1. In a portable percussion tool, the combination of a reciprocatorypercussion element, a motor connected for operation of said element, ahousing for said hammer element, a housing for said motor adjacent saidelement housing, said housings having adjacent faces along a planetransverse to the path of reciprocation of said element, a shockabsorbing and vibration damping gasket interposed between said housings,bolts extending through said gasket for removably fixing said housingstogether, and another shock absorbing and vibration damping gasketassociated with some of said bolts, both of said gaskets beingsimultaneously compressed by the tightening of said bolts to fix the onehousing with the other.

2. In a percussion tool providing a hand-grip portion at the one end anda tool receiving socket at the other end, the combination of a-motor, areciprocable hammer element adjacent said socket end and adapted todeliver percussion blows against a tool held in said socket, atransmission connecting said motor for reciprocation of said hammerelement, a frame housing said hammer element and transmission andproviding separable portions having faces adjacently arranged relativeto a plane transverse to the path of reciprocation of said element, ashock absorbing and vibration damping member interposed between saidfaces, means fixing said housing portions together and simultaneouslycompressing said member toreceive thrust of one of said housing portionsin one direction, and another shock absorbing and vibration dampingmember compressed by said means and positioned to receive the thrust ofthe last mentioned housing-portion in the other direction.

'3. In a percussion tool the combination of a housing, said housingincluding portions having adjacent faces along a plane transverse to thepath of reciprocation of said element and between said hand grip and theexposed portion of said element, a shock absorbing and vibration dampinggasket interposed between said adjacent faces for; compression by forcestending to reduce the spacing of said faces, and another shock absorbingand vibration damping gasket adapted for I compression by forces tendingto increase the spacing of said faces.

housing providing a hand grip at the one end 4. In a percussion tool thecombination of a there0f,- a reciprocable percussion element having aportion exposed at the other end of said housing, said housing includingportions having adjacent faces along a plane transverse to the path ofreciprocation of said element and between said hand grip and the exposedportion of said element, a bolt continuously urging the one of saidhousing portions in the direction of the other, and shock absorbing andvibration damping gasket means including a gasket portion interposedbetween said faces for compression by forces tending to reduce thespacing of said faces and another gasket portion associated with saidbolt for compression by forces tending to increase the spacing of saidfaces, each of said gasket portions being simultaneously compressed bysaid bolt.

ROBERT T. FETHERSTON.

